Nothing wrong with PU making this call, although like basketball - this is your partner's primary, so I'd hesitate half a second before calling it, in case he saw it the other way around. Worst thing you can have here is him calling INT and you calling OBS. Sounds like OBS to me too - but you don't want a blarge.
Coach deciding to hold the runner should not have an iota of bearing in whether you send this runner home or not - coach's decision was made AFTER the obstruction and was based on where that runner was and where the ball was at the time he made that decision.
Would she have scored absent the OBS - that's ALL that should matter to you.