Unlike Dorothea, Celia nature readily aligns her views with the mediocre prejudice of her influential friends, foremost among them (the rather self interested) Sir James Chettam (
Sir James never liked Ladislaw). For instance, Celia is happy to prejudge the motives of Ladislaw and Lydgate. Dorothea mistakes are not those of ethical mediocrity, but those inherent in the forgiveable idealism and naivete of youth.
Does Dorothea forsake her ambition for love? She marries Ladislaw...for love. And lives happily every after it seems.
Your interpretation of the closing paragraph of
Middlemarch seems at odds with the literal meaning of the text.
Her finely touched spirit had still its fine issues, though they were not widely visible. Her full nature, like that river of which Cyrus broke the strength, spent itself in channels which had no great name on the earth. But the effect of her being on those around her was incalculably diffusive: for the growing good of the world is partly dependent on unhistoric acts; and that things are not so ill with you and me as they might have been, is half owing to the number who lived faithfully a hidden life, and rest in unvisited tombs.
I understand the text to say that Dorothea retained all
her ambition for love but that societal opposition, reduced wealth and the subservient role of women redirected her once grander efforts into a myriad of small, yet noble, channels. As Lydgate, Ladislaw, Farebrother and Rosamund had been blessed but Dorothea's angelic touch, so her future loving but
unhistoric acts would make things
not so ill with you and me. She was born and remains an angel.