I think that the terminology used often gets in the way of talking about this issue. People have very strong feelings about words like Mother, Father, Love. I tend to try to think past the words to the core feeling. The fact that your T isn't your mother, and never can be, doesn't necessarily mean that she can't have motherly feelings for you, and you for her. What you both do with these feelings is what's important to determine. If she is willing to engage with those feelings and you are willing to accept rather than fight against them, it can be a very healing experience.

Where I think the difficulty comes in is when the T either doesn't have those feelings or has them and is uncomfortable working with them; or when the client has them, but denies them, and fights to "get past them" rather than getting through them.

I had those feelings as did my T (paternal rather than maternal) and was fortunate enough to have a T who was knowledgeable, secure in his boundaries, and adept at engaging with transference and counter transference. It took me a long time to stop fighting it and risk allowing myself to be that vulnerable, but it was probably the single most important aspect of my therapy. He was able to help me experience fully and then resolve the transference.

Of course, you cannot control the counter transference, if there is one. But if the T is well-versed in working with transference, I think there is much to be gained by pursuing the emotional experience. Once fully resolved, you will no longer feel the compelling need to be mothered, yet you will be able to accept such feelings where offered.