How can I help my best friend /: ?

My best friend is awesome.We usually like only hanging out together like we don't have a group of other friends, therefore we are very close.She calls me a lot and often complains about how her parents freak out about nothing.Like her parents once grounded her for going out during a storm.I mean really?Also, there going on vaca and I said I could possibley pet sit while they were away.I NEVER told them it was a certain yes.Anyways, my mom told me I couldn't because I would have school then so I told my friend I couldn't over the phone and she told her mom (who must've been pretty close by) that I couldn't. I heard her mom FLIP OUT and she was saying how she couldn't trust me and blah blah blah.I wanted my friend to hang out the next day but her mom still said she couldn't trust me. A lot of the times I ask to hang out my best friend can't because of really lame excuses.Also, whenever we CAN hang (which is rare) her mom makes my parents do all if the driving and stuff. My best friend has seemed really down lately and I'm pretty sure she'll end up being really depressed if her parents keep her locked up in there house all summer and if her parents constantly flip sh*t on her for really stupid reasons. How can I keep her from being depressed by this if she can never hang. We can ony call and text really anymore )':