May I sign my elderly mother's checks for her?

My 95-year-old mother recently finds it impossible to sign her name. She has problems with "executive function" and arthritis. She understands what she is signing, but can't execute the signature. For a long time I've been writing her checks for her to sign, but she would sign them (barely legibly and with great difficulty). But now she can't focus on the activity long enough to complete it. Is it OK for me to sign her name, and then annotate it underneath (by [my name] POA). She only writes 1-2 checks per month, one of which is to me to reimburse me for her expenses in the previous month. She lives with me, in Maryland; and we have always maintained separate finances; I have her durable POA. (I did add her name to my checking account years ago before I retired, but only as a convenience, so she could pay service people while I was at work; all the funds are my own. My name is not on her checking account, which is where her Social Security deposit--her only income-- and automatic Medigap payment are made).