hey welcome.
right, need a bit more information.
has this been since when she was a puppy.
does she know she is peeing
when does it happen etc when she is exited,nervuse, playing, before/after a walk, when you in or when your out
what was your atempt at toilet training her as a puppy, e.g. puppy pads, papper, leaving the door oppen to the garden allday, bell at back door.
how much does she eat and drink, at what times is she fed, and what times is she walked(i know you she is walked 3 times a day but at what times)
is she crated.
the best advice is to go back to basics, she wont be doing it intentualy, it will be a case of her not knowing that she isnt ment to pee in the house. the best plan of action is to go back to basics, treat her like a puppy again, even if it means taking her out every 20 minutes, then lengthoning the time between trips outside. making a big fuss when she pees on the grass.
if she is peeing when exsited i.e. when you or anyone walks in the front door. you need to just not talk to her at all. she will be getting over exited that someone is talking to her and will lose controle of her bladder.
if you dont talk to her she will have nothing to get exited about. only talk to and pet when she is calm. (noy an instant fix, takes a couple of times for her to get that noone talks to her when they come in.)
hope some of that helps, if you can answer some of my questions i may be able to help further.