I think her character caught on, as so often happens with tv in general, more than the showrunners originally thought she would. I don't think they ever intended on her being a regular, but the actress has alot of personality and great chemistry with Grant , and her character went over well with alot of the fans, more so than Linda did imo.
You also have the added problem of late feedback from the audience since they film these episodes way ahead of time without really being able to judge how the audience will react to certain characters. By the time the episodes air the season is usually mostly in the can, so they can't really course correct in real time if a character like Patty is popular and the fan reaction in negative to removing her from the series.
I have no doubt she'll be back in the future , but hopefully if they do plan to introduce yet another non Iris love interest, they'll try to take their time with it and not try to rush the relationship or the character out of the door.