I need a heads up - when will my pup let me know that she needs to 'go'?
My 3 mo old border collie maggie does very well when I take her out to potty or if I leave a door open she will go out on her own. The problem is at night when I don't wake up to take her out.
Is there a way to train her to get my attention when she needs to go?
Hi Maggie is doing very well to be so reliable at only 3 months old, so give both yourself and her a pat on the back!
However, the fact that she's not letting you know that she needs to go in the night time is a problem.
If you're not already using a crate, I would strongly suggest getting one, and crating her at night. She won't want to eliminate in her crate and will likely bark/whine/cry to get your attention so that she can go outside. My Crate Training A Puppy page has tons of tips and advice to help you with this method of housebreaking.
For other times, you could try to train her to use a bell to let you know that she needs to go outside. There are a couple of options that you can look at here. One is a small 'chime' unit that you put on your floor or wall-mount and you can teach your pup to activate it by using her paw or her nose. You can see it here Lentek Pet Paw, Additional Paw for Pet Chime (This option is good for doors without handles, such as sliding/patio doors)