Definition "unreserve" in this content

[post]

Hi

The following is part of the novel "Emma" by Jane Austen:

but the intercourse of the last seven years, the equal footing and perfect unreserve which had soon followed Isabella's marriage on their being left to each other, was yet a dearer, tenderer recollection.

Would somebody elaborate the meaning of "unreserve" here.

Thanks.

[5jj]

Openness, frankness, lack of reserve.