Any experience with Lexapro for Alzheimer's patient?

Has anyone's loved one with dementia been prescribed Lexapro, and did it help their anxiety and depression? Mom, 92, with mixed dementia (Alz. & vascular) was started on Lexapro a month ago and shows signs of improvement with anxiety, but not with depression. I am grateful for the reduction in hostility, agitation, and verbal outbursts so far, and if we can attribute those improvements alone to the Lexapro, it's more than worth it; however, just wondering about others' experiences with this for their LO and if it took awhile to be effective for depression. Mom's doctor said it might take as long as 3 months for the Lexapro to take full effect.

Thank you in advance for your input! This community is wonderful!