I'm not completely sure on this intriguing point.

There appears so much in the novel about secrecy and the nature of feeling.
Brandon's love of first Eliza allows him not only to tell Elinor of his past but to reveal the depth of his feelings;
'he could say no more, and rising hastily walked for a few minutes about the room.'

The second Eliza is her daughter entrusted to the Colonel's care whom he accepts as 'a precious trust.'
After Eliza's seduction and desertion by Willoughby, she remains under Brandon's care and protection.

Elinor agrees with Col. Brandon his account of Willoughby's despicable behaviour may help Marieanne recover from her infatuation.
'I have been more pained', said she, by her endeavours to acquit him than all the rest; for it irritates her mind more than the most perfect conviction of his unworthiness can do. Now, though she will suffer much, I am sure she will soon become easier.' (ch.31)

The lives of the two Elizas parallel each other in many ways. Yet if the first Eliza reminds us the Colonel is a man of feeling; Perhaps the second Eliza shows us he is also a man of honour and her sad story gives us sympathy with Marieanne regarding Willoughby.