Ex-boss of ten years now an elderly senior and emotionally needy with me.

I so hope that u come back and tell us how u end up handling this situation. We learn from each others experiences.

If she retired 10 years ago, does that mean she's about 75 years old now?

It like it was a weird relationship to begin with. I'm not sure that grief causes people to lose their awareness of social cues, so maybe she wasn't good at relationships to begin with and she's got something else going on, like mental illness/depression in the mix. If anything, someone with early-ish signs of dementia/memory impairment usually make a mess of their phone/address contacts (this happened in multiple of my family members, and am watching it happen to my Mom now). So, she is still able to do some very specific things, including driving herself to meet you places, which would make me personally think it is probably not dementia.

Without going to her home to see if it is in disarray (another sign of dementia/depression), you have no way of knowing what's really going on. You don't have any obligation to do anything, but out of mercy, if you want, you can report her to APS if you know her address (and tell APS you'll be blocking her). Then have peace in your heart that this is as much as you can do for her.

I think you answered your own question. She is grieving and she doesn’t have any family. She’s struggling with her emotions.

Have you thought about suggesting grief counseling? Or maybe she could participate in a grief support group such as griefshare.org.

Tell her that you are busy when you don’t have the time to chat.

Why do you suspect that she has dementia? Have you noticed different behavior before her husband died or is it only recently?

You have someone to look out for

If she truly has no family whatsoever and she has dementia, it would be a kindness to get her on the radar of Adult Protective Services. Imagine how terrifying it is to be alone with dementia. No wonder she freaks out when you aren't in contact.

Contact APS on your own and ask them what they'd advise. Make it clear that you are not able to take on her care or supervise her care. She is simply a vulnerable elder you're reporting.

You can do this anonymously so she doesn't know who called.

I would call APS in her area and ask they do a "well check" based on what you said here. The death of her husband may have caused some kind of episode. Ask that APS contact you that if they find there is nothing wrong, you will need to tell the woman what she is doing is harassment and it has to stop. Your relationship was never more than two women who used to work together and have kept in touch. You have no idea why she suddenly feels you owe her anything but you don't. You are not that kind of friend and really don't want to be. If then she continues to email, or call and or text you can block her. So hope that APS will be able to tell she has Dementia. Maybe if they talk to neighbors, they too will say she has been like this since husband died. Maybe her covered up her symptoms.

I really don't understand why people are so reluctant to be gently honest.
I have two ways to do this. The honest way and the easiest way.

For honesty:
Dial the phone.
Tell your friend "I have to tell you that I am so sorry. I am not able to talk with you any more on the phone. I hope that you will find support where you live or that you have friends, family or a faith community to reach out to. I simply don't have time and I am already neglecting the friends I have. Do know that I wish you well."

For easiest way:
"Irene, I am so sorry, but I just cannot talk on the phone with you. It honestly hurts my ears, and I don't speak on phone even with family. One ear is almost deaf and the other hears things at a different tenor on the phone that I find disturbing.
Know that I wish you well."

This honestly is intrusive. If you wish to be nice those are the ways to do it.
If not tell her that you cannot accept her calls any more and block her.

Well, I think there is a middle ground between blocking her and picking up every phone call.

Encourage her to find friends

Block her phone number and discontinue responding to her emails. That's the simplest way to cut ties with this woman, especially if she has dementia, because you cannot use logic or reasoning with such a person. You'd tell her 1000x you don't want contact, and she'd contact you 1001x. It's a losing battle. And, if she's suffering from dementia, that's precisely why she's so clingy with you all of a sudden.

If you wind up speaking with her agai for whatever reason, perhaps suggest she get to her doctor for a full physical because she seems a bit off lately..not like her old self.

Good luck to you.

Tell her you're going away for an extended vacation (two months? three?) to "Timbuktu" and will not be able to be in touch, hopefully that will give her time to break the habit of contacting you.