I know how frustrating this issue can be. I am a SAHM so I'm home 99% of the time my dogs are out and always quiet their barking if it gets out of control. I remember being at the animal shelter once and there was a lady in there being lectured by the pound from neighbors coplaints on her dogs out of control barking all day. They were very firm with her and told her she had to ge it under control whatever wahy she could.
She was very upset but it must have been frustrating for her neighbors as well with her getting so many complaints. So if it comes down to it in your situation, call the city pound to make a complaint or even the non emergency police line to report daily noise disturbance. They can do the dirty work for you w/out her knowing anything about you being the one complaing.
Do you know if she is home "during" the barking episodes? If she's home that would really frustrate me and is rude and disrepectful of her letting them get away with that. If she's not home,she may have no idea there's a problem and that's when a friendly note from you or knock on the door to let her know would come in very helpful.
Back when me and my husband got our first apartment together, we weren't aware of the barking our small dog was doing "while we were gone". She was soooo quiet when we were home so we didn't realize she was barking and howling while we were gone! : ) So one day we came home and found a very nice note from a neighbor who told us she lived directly downstairs and the entire time we would be gone, the dog would bark uncontrollably.
We felt terrible and were so embarrassed and immediately apologized. We found a different area of the apartment to house her in while we were away and it solved the problem. Neighbors happy as well as us, we never intended to let her bark like that or disturb anyone which is why it's important to find out when the dogs are behaving this way and I don't think a note to her so she's aware will cause any feuds.
IF you don't feel ready to bring it to her attentiion, I again recommend you calling your local police dept (non emergency) or city shelter and seeing what they can do or recommend.
Good luck to you, I'm sure everything will work out fine!