What to do...

OKay so on my facebook profile I put that I love my job because if you do your best & try hard that you will get called back. So there is a teacher who just found out (like right before school started) that she has breast cancer. Last year she would always try to request me but I was always booked for another class. So this year started off-the first four days of school & I sub two of them! both are in her class-one for her & the other for a s.p.e.d student who is in her class & needs an E.A. with him at all times. So b/c I have been in her class & am one of her favorite subs she requested that I be the sub to take over while she has radiation therapy & surgery for almost two weeks (if everything goes well...). Here's my problem: At the begining of this week my mom called me to ask if I would be willing to drive my grandparents to CA for a funeral & I was willing to drop everything to take them. As it turns out Papa said they would be fine & Marm said that they would stop through on their way home.... So! I have no clue when they are planning on heading home (they have an idea but with Papa you never know!) Marm told me not to worry about trying to take days off for them being here but that they would take whatever time they could. So then all of this comes up with this teacher & so I called my mom about it & told her that I need to know when Papa & Marmie are planning on coming through (cause I am booked every day for the next three almost four weeks!). My mom got upset with me!! What do I do?!?!?