It depends. Assuming her existing TB coach is fine with it depends on the local association. Here until Memorial day the rosters are pretty loose. Elsewhere things may be different. Your existing TB coach should be fine with her getting some extra playing time, but I would strongly urge you to extend the courtesy of a conversation before she guests.
It may be different in other areas of the country, but in GA pick-up players are pretty common and the only stickler for rosters is ASA in qualifiers. Everything else is pretty loose as long as the player is covered under the teams insurance waiver. A lot of teams us pickup players in tournaments as part of the tryout process. There are a lot of cage hitting phenoms who wilt under pressure against live pitching in a tournament.