Is this "friend" taking advantage of/using me?

Okay, so I am a mom to a 2 1/2 (3 in July) y/o little girl, right, and of course I now and then want fellow mom friends. So I made this friend almost 2 years ago who I met at a library. Her daughter is just 9 days older than mine. She's a single mom to 2 daughters both from different fathers---one is almost 17. The little one the father is a military guy and jumped ship on them, never seeing her since 7 mons old etc. and just sending the monthly child support. So basically she doesnt have a lot of help although she does have sooo many friends, and her mom and dad and stepmom who often watch her daughter for her while she works. She didnt actually start working til her daughter turned 18 mons (same as me). She used to never ask me to watch her daughter and would do favors for me like let me in under her membership to places like the zoo, saving me money and giving me and my daughter a free outing, but the compensation was we'd go in my car and use my gas. well last year in dec. I lost my job as a substitute worker because of budget cuts, so basically she who still had a job, started asking me if I could watch her daughter. I said yes once for a couple of hours for free at her place, driving to where she lives which is about 20 min away, 30 with traffic.

anyways the yes became another yes etc. so basically once a week or so I;vwe been going to her place since about jan.watching her daughter for free. now and then she'' give me 5-10 dollars for the 2-4 hours i'm there. I bring my daughter with me bc they.re friends and my daughter has so much fun over there with all of her toys like playhouse, etc that my daughter doesnt have.

well i only work part time somewhere else now and it;s not much money. I'm looking for a better job, and money is an issue with me even though i "have somebody" as she puts it. IShe knows about my financial situation too, just like I know about hers.

now and then she'll offer to watch my daughter, she did yesterday, but it always has to be at her house and it's always for 2 hrs or less. She does work every afternoon.

i have mentioned her coming down to see us instead but she said she was too scared of my neighborhood (what?)

It just kinda makes me mad bc here I am making hardly anything and watching her daughter for free. She makes more than I do although it does all go to rent and her 2 daughters esp. her odler daughter who goes to a private school.

Last week she made almost 1,00 in one week and my first thought was, "you cant give me any of that for watching your daughter one day?"

Here's another thing: she's so stingy about me taking any food or drink for myself (sometimes even for my daughter) even though i'm there for almost 4 hrs once a week, and she gets food stamps so groceries are free for her.

Oh, and this also bugs me: often times she'll go out to eat etc with her other girlfriends but not invite me which to me is rude. One time she just got off and her friend came and they were gonna go to a restaurant making plans right in front of me without even asking if I wanted to come, after I just watched her daughter at her house for FREE. Now and then we do go to parks together etc. but that's it. Oh and sometimes she invites me to the museum with her and lets me get in underr her membership but it's almost always followed by "can you watch her/"

The reasons why I do this and allow myself to be treated like this are because 1--my daughter loves it there and often asks about her daughter (But I would rather feel like a friend over for a play date rather than a babysitter) 2---I do genuinely adore her daughter and feel bad for her, having a single mom, no father figure etc. 3---I desperately want to keep the few friends I have esp. mom ones (but at what cost?)

Does it seem like she's using me? any advice?