Last derelict
 

"Lady Frances," he continued, "is the sole survivor of the direct family of the late Earl of Rufton. The estates went, as you may remember, in the male line. She was left with limited means, but with some very remarkable old Spanish jewellery of silver and curiously cut diamonds to which she was fondly attached--too attached, for she refused to leave them with her banker and always carried them about with her. A rather pathetic figure, the Lady Frances, a beautiful woman, still in fresh middle age, and yet, by a strange change, the last derelict of what only twenty years ago was a goodly fleet."

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Do you think the red part is ambiguous?My interpretations seem to hold good:

1. The last derelict=Lady Frances still has some beauty in her, but not as much as formerly (=20 years ago,); 20 years ago, she was very beautiful. (=a goodly fleet)

2. The last derelict=Lady Frances is the only rich one in that direct family. 20 years ago, that family was properous and affluent (=a goodly fleet), but no longer.

To me the red part is not ambiguous, but neither of your interpretations is correct. Of the two, the second interpretation is better. I understand it as:

The last derelict = Lady Frances, is the last member of the direct family who is still alive. She is not rich now, because as a woman she did not inherit; some male cousin inherited, leaving her with little money. The goodly fleet was her father the late Earl of Rufton, his wife, and Lady Frances's many siblings, but they are now all dead.

Thank you~