My friend likes to treat me when we go out, but I'd rather we pay only for our own share, how to deal?

I am not a big eater nor big spender, especially since I lost my job a few months ago. Likewise, I avoid going to restaurants and suggest places with happy hour so I can spend under $5. This works with MOST friends. But I have this one friend who eats/drinks alot, her part of the bill ends up being $20-30, she inevitably offers to foot the whole bill (since my part is so small) and is really stubborn about it! I am not equally stubborn and let her treat me some of the time, but I can't let her all the time. Last time, I insisted that I pay my share ($5) but she refused really stubbornly and I ended up insisting on treating her! Which was alot more than mine, about $25. And this was probably awkward for HER since she knows that I'm unemployed & trying to economize. And while normally I'm happy to treat friends, I AM unemployed and would rather just pay for what I get and not have to think about treating others and getting treated. I know she's being nice and I'm not so proud as to refuse all generosity, but I don't think it's really generous when the other person really doesn't want to get treated. She's one of my best friends and I will flat out refuse to let her treat me, she knows I don't want her to treat me, but she'll insist on it any way. This has gotten awkward for me. What can I do?