Frustration

I am so completely overwhlemed right now. I have a lot on my plate and last night my mom in her oh so lovely way added another heaping spoonful of guilt. Scott says I should just consider the source and forget it, but she is my mother and I hate it that she thinks I don't appreciate her. I try SO hard to make sure she knows I am grateful that she watches my kids two afternoons a month. She's mad because she feels like all she does is "give, give, give" (her words, not mine) and she get's nothing from us in return. I just feel so bad. I'm not sure what she wants me to do. I always say thank you and we have her over for dinner and try to include her in everything we do. She wants me to take her to the airport next week, but I can't - I have to work and can't take time off right now. I am picking her up the following week, but that doesn't count apparently. She also wants Scott to mow her lawn, which just isn't fair to ask of him. He's working 6 days a week right now - 10+ hours on weekdays and until late Saturday afternoon. He can hardly keep up with our yard and she is acting like he just won't help her. I just feel like she only helps me if there is something in it for her, otherwise forget it. I just wish she'd watch the kids because she loves me and loves them. It really doesn't feel that way. In fact, now she says she wants to move to St George, but can't because I need her (then why did you already buy a lot to build on here?). I do need her, I need her to stop acting like a 2-year old and get some help. She is not coping well with my dad's death, but it's been 2+ years now. She is so negative, my kids don't even want her to tend them. I've got to figure out some other options. It just isn't worth ruining my relationship with my mom.
Last night's phone call with her was so frustrating, it made me cry. I miss my dad and I feel like not only did I lose him, but I lost a big part of my mom too. I just don't know what to do.