I am not a fan of crates for long term storage of dogs. Dog crates sized so your dog can do no more than stand up, turn around and lie down would be banned at most zoos.
If you are only worried about her trying to bolt out the door when you leave then I suggest a heavy duty dose of training in manners for that dog. Failing that (though you should do that anyway
) can you not simply shut her in a room and Then your mother lets her out?
If she is going to be crated for more than a few hours then I would get the biggest crate I possibly could. Large enough for her to stretch out two times over so when one spot gets hot from her body heat she can move to a cool spot.
What I did when mine were puppies was put the crate, with the door open, in a big pen we built or in our gated kitchen. Warning, gating in a room may expose that room to considerable damage as dogs might eat costly hardwood cupboard doors, chew through drywall and even badly injure themselves. However we did not have any of that.
We made our own gates, they are much sturdier and higher than any baby gate you could ever buy and I suggest you go this way, if you do at all, with a dog as big and powerful as a Rottie. My dog is a Lab, those gates are still up, they are handy for containing Mr. Muscles while he dries off after a swim.