My advice would be to cut it entirely back to the crown and allow all new growth to slowly emerge. The new fronds will be acclimated to the indoor environment. What you are describing is rather normal behavior for a boston fern moved from the outside to inside.

Don't increase watering frequency unless the soil is evaporating more quickly. Adding a humidifier to the 'fern room' would be helpful, as that is the one limiting factor you have not mentioned. They like humidity, but misting can cause disease problems in Boston Ferns. Remember, misting is not a good method of raising humidity....it justs wets the leaves for a short time.