In Ltr. 64 Jane is staying in her brother’s home in Southampton but Frank is in Portsmouth with the St. Albans and I believe the hopefully detained ladies are his wife Mrs. FWA (nee Mary Gibson) and a cousin of hers—Miss Curling, see the Biographical Index of JA’s Letters (Le Faye), page 514. It seems Miss Curling is the thorn rather than Mrs. FWA:

In the first place, Miss Curling is actually at Portsmouth, which I was always in hopes would not happen. I wish her no worse, however, than a long and happy abode there. Here she would probably be dull, and I am sure she would be troublesome. (Ltr. 62)

Jane also writes the St. Albans (thus Frank) “may soon be off” to Portugal. I suppose in that event Mary would return home to Southampton and to Jane’s gentle vexation with Miss Curling in tow. So I think when Jane writes “I dare not hope that Mary & Miss Curling may be detained at Portsmouth so long” she is expressing a wish to delay suffering Miss Curling’s company herself. Jane relates some trouble on the lady’s account but if it is by the lady’s efforts or by that of the Navy, Frank or Mary I am not sure:

I had a nice brotherly letter from Frank…No orders were come on Friday, & none were come yesterday…I had supposed Miss C. would share her Cousin’s room here, but a message in this Letter proves the Contrary; --I will make the Garret as comfortable as I can, but the possibilities of that apartment is not great. (Ltr. 66)