Keep in mind that you are only describing a single indoor accident in 4-5 months, so this really wouldn't be too unusual or remiss. Generally, most dogs are not reliable until about a year of age. Also they tend to be a bit up and down at this age -- which is dog adolescence. They also tend to 'forget' a lot of basic obedience training etc around now too.
Once you eliminate any medical reason, the best approach is really not to assume you have a housetrained dog til she is about one and to manage access. This is especially true if you have rugs/carpet you don't want damaged -- it truly is better to take a conservative approach and assume you need to remain an active supervisor and manager of your (still very young!) dog. After all she still qualifies as a mere puppy at this age.
I always think people also need to remember that owning a dog means it is best not to get to upset at the odd accident and not to be too houseproud. Along with a lifetime of hair in and on everything
, you WILL have accidents inside, on and off throughout the dog's life, for reasons ranging from illness or a move to a new unfamiliar house to simply not getting our dog out in enough time when they have to go. It's good to always have some enzymatic cleaner in the house for the odd accident to prevent stains and smell and the animal returning to the same spot to go again, because the one thing a pet ownr can expect along with all the unconditional love is poo, pee and vomit now and then on the furniture, rugs or carpet. :grnyuk: The joys of dogs! I had Lily once both have the runs and throw up while I had a friend over for dinner... what a charming addition she made to the evening!