Fishlock suffered the injury late in the team's April 24 road match in Boston and it was originally estimated that it'd take 4-6 weeks to recover. She was still on crutches and in a leg-brace as recently as last weekend's home match against Portland, but evidently Wales manager Jayne Ludlow was convinced that she could be ready in time for the international match.
June 7th is just over 6 weeks away from the injury, and given the need for a week or so to train ahead of the match, it sounds like Fishlock is right on track in her recovery.
Wales' chances of qualification for the Euros is currently hanging by a thread, and a home win over Norway -- the group leaders -- is close to a necessity. The Dragons are in third, five points behind both Norway and Austria, in a group in which only the top two advance. A Wales win in June and Austria losses to the Norwegians and (admittedly less likely) Israel would put the Welsh in position to leapfrog into second with a home win over Austria in their September match. A loss combined with more points for Austria would effectively end their qualification campaign.
The next Reign match after the internationals will be June 12th at home against Houston, which (if all goes as planned) will mark the return of Fishlock to a midfield that desperately needs her, having scored only two goals in the three matches that she's been absent.