Sometimes, their urinary sphincter muscles don't work as well as they should, especially in this breed and with the spay history that you mention. If this is the case, there are medications that can help to improve sphincter tone. You should talk with your vet about them.
Also, urinary incontinance can be a sign of a disc or back problem so you will want to have this checked by the vet as well.
My last thought is that she has a urinary tract infection or or urinary stones that might be causing a blockage.
No matter what, you need to see the vet about it. You don't want to take any chances as a pet ages.
If finances are a problem for you (because you stated that you want to avoid a vet), you might want to look into www.carecredit.com. They offer financing for large and small vet bills.
Let me know if you still have questions.