Two sentences. Which one would you choose?

[Kaitlyn Wadsworth]

For a while, she was the only one he can trust and rely on.
For a while, she is the only one he can trust and rely on.

What do you think?
Grammarly accepts both.
Personally, I think 'For a while she was the only one he could trust and rely on.' (could sounds better than can here)
Online Book Club says one of the above is incorrect. Which one? I still disagree.
10 points down for that even though it wasn't incorrect! Shocking.

is or was? I believe 'is' is better.

[Mafusi Cynthia Maine]

For a while, she is the onlyone he can trust and rely on

[Kaitlyn Wadsworth]

Thanks for this reply. It has confirmed the dilemma I am in.

I actually made a mistake in the question and the alternative did have a 'could' in it. However, my contention is that even if both are correct, it is still a personal preference issue. Not an inaccurate grammar issue on my part.

[mazen2008]

For a while, she was the only one he (can) trust and rely on.
but the use of 'could' instead of 'can' is better.

[Runan]

I think ‘for a while’ can be used in any tense, so both sentences are correct. For a while denotes an action that occurs for a particular duration of time. ‘In a while’ is future tense.