Can ignorance be a reason to accuse someone for trespassing?

several weeks ago, i was staying with my girlfriend in her house, which she shares with her brother and her younger sister, all of whom are over the age of 18 and is an add on to her grandmother's house but with no access to the main house. the building is a 3 bedroom "condo" which was an added extension of the garage. now, my girlfriend had given word to her grandmother that i was going to be staying a few days with her, which she had ok'd. in the course of these several days that i had been staying there, my girlfriend's soon to be ex husband (they're currently going through a divorce) had stolen my cell phone and destroyed it, preventing me from getting in contact with a friend or family member who could give me a ride home. on the third day that i had been staying there, after my girl and i had woken up, we were sitting outside smoking a cigarette when her grandmother came rushing towards us and had got in my face, telling me that i was not welcome there and that i was trespassing, and that she had told me several times that i was not welcome there, when in fact she made no such statements directly towards me but had told my girl that she did not want me there, but that was before my girlfriend had told her grandmother that i was going to stay a couple of days there until i could get a ride. after she was finished with her "barking" she informed us that she was going to call the cops and have me arrested for trespassing. her grandmother knows hardly anything about me, mainly for the fact that she will disregard anything that my girlfriend tries to tell her, in her mind, the fact that i smoke automatically makes me a bad person. however my girlfriend has tried to tell her grandmother that i have served in the military, that i was a volunteer firefighter, and that i have plans to join the police force for the next county or to become a paramedic, as well as the fact that i have a spotless criminal record, so quite honestly... nothing about me or my past is bad. and yet just because of sheer ignorance, her grandmother has tried to have me arrested for trespassing on the property twice for no legit reasons. in the state i live in, in idaho... i can only be arrested for trespassing if i do not have permission or haven't been invited onto the property, which i have by her granddaughter. my question is... can she accuse me and charge me with trespassing, if i have permission to be there by my girlfriend, her sister, and her brother?