My brother (US citizen) is currently dating a girl he met in El Salvador while he was living there. She has a B2 visa that was recently renewed for 10 years. They entered the US last month with the intention to spend a few months there, traveling and visiting family she has. My brother has Global Entry and says they asked them very few questions when entering (destination in the US, if he will cover her stay financially). They wanted to stay the full 180 days permitted with the visa, however, they recently met with an immigration attorney who advised them to stay 90 days max. She also said that if they want to stay longer in the US, they should get married and apply for AOS.
My brother states his girlfriend's main concern is not have problems with her existing tourist visa, and be able to remain in the US for the time permitted without raising flags. He says he is feeling pressured to pursue other options (marriage, AOS) due to the current immigration situation in the US.
My question is this:
Will a longer stay on the B2 visa raise flags, and potentially cause problems should she wish to reneter in the future? She has a few previous trips for shorter durations prior to this.