My wife is spotting 6 days before her scheduled period starts?

My wife is really worried because this is the first time she has experienced this since coming off her IUD 6 months ago, so I’m trying to alleviate some stress off her as she is worried something down there is wrong.

This weekend she was telling me about her breasts being sore, she thought she was getting close to her period so I went out and bought her some more pads and snacks of course. And Saturday we had intimacy. Sunday she told me she might have a UTI as her urine was burning while coming out so she took some medication for it and we waited it out.

Today she came home, and everything was good besides some cramping she said she had, she was talking with her mom on the phone and then went to the bathroom, came out and reported that she had bled on her underwear. A big spot both brown and red She immediately looked at her app that tracks her cycle, and said her period isn’t supposed to be here until Sunday.

Anyone know what this could mean/ or if this is an issue we should take to a doctor. Could something have happened to cause this? (She is eagerly waiting answers)