Tell her to bring the truck back, tell her that her car problems and the OM's vehicle inadequacies aren't your problem and because she couldn't respect your request to bring it back on time you won't bother loaning it to her in the future.
If she borrowed a vehicle from a friend and the friend asked her to bring it back by a specific time, would she have brought it back on time or would she have taken her time and stalled and return it late?
If she can't respect you the same way she would respect another person offering the same thing to her then she can't borrow from you anymore.
Stand up for yourself, you're allowed. You don't have to be a prick or an a$$hole but you do have to stand up for yourself.
And what's this about the OM driving her and your kids around? UMMM.... NOPE! You didn't agree to him driving your kids anywhere, she can do whatever she wants with him but not with your kids.
