If I can give my two cents to this topic...
I want to tell you a little story.
10 years ago I was offered a place in a new private degree program. Only 15 people all over Europe were accepted and it was expensive, 14 hour days (so no way to work a job to earn some extra money) and it was very exhausting. I knew, I couldn't go because I was 24 and didn't just have the money that I needed for that on my bank account. But you know I am a Christian. (And sorry if this is inappropriate on this board but it's important to the story) Some of my friends thought that it was God's plan for me to go and take part in this program.
They told me - Go and God will provide.
Well, I decided to put that to the test and accepted and was ready to travel to the country and city the program was held in. I had to find a place to live, find enough money to pay my health insurance and living costs and on top of that the tuition costs.
At the airport, shortly before going through security I got extremely anxious. I thought - what the heck was I doing? I have absolutely nothing except the first month of rent.
I heard someone calling my name. I turned around and about 20 people, friends and acquaintances stood there waving at me. Everyone gave me an envelope with money with strict instructions to only open it when I had arrived. A couple I knew took me aside and told me they were going to pay the whole year for me, that they would put $1600 into my bank account each month. I was in shock and didn't want to accept it, it wasn't like they were incredibly rich or something. This was quite a percentage of their income. I cried and said no and felt horrible.
Then the husband said: It takes strength to accept a gift of money. It takes more strength to believe you are worth it. And it takes even more strength to believe that we do this because we love you.

I had an incredible year and got my degree and finished second best in my class. And I never had to pay back one penny, even though I felt I had to. But it was a gift.
HG, I believe your T is giving you a gift. And I think it will help you grow and heal if you accept it. Because, what if you don't? Then for two months you will miss her, you will be anxious, you will feel alone, you will carry burdens by yourself. But if you do accept her offer, it's a great opportunity to learn to accept that your worth it, that it's ok to accept a gift like this. If she offers, she means it. If she means it, she cares. If she cares, you can allow yourself to care back :-)
Don't beat yourself up so much over this, HG. You are a wonderful person, why would you not deserve this gift?

Maybe you won't always be in the position of not being able to pay. If she takes you on pro bono, she can probably use it as a tax deduction.

It's okay to feel anxious over something like this, but I think the best thing that you can do is let your therapist talk for herself. In situations like this, often our fears and worries come to the surface (and it's good to be able to work on them in the therapy), but what we think and feel belongs to us, not our therapists. We can’t read their mind or decide that we are taking advantage of them, only they know that.

Try to remember what your therapist has said about this herself. If she's offered, then I expect she's completely okay with it. The one thing that does actually annoy my own therapist a bit is if she makes a generous offer and I turn it down because I think I'm doing what's best for her. Sometimes I know it makes her feel like I completely reject her generosity when she's been willing to go out of her way for me.

I also started the year off with a $3000 dentist bill and lost a source of funding that contributed to therapy fees, so I've had to reduce my sessions, which has been really hard on me. I really hope you're able to enjoy and appreciate what your therapist is willing to do for you, even if you do have some concerns about it.