Short answer: No, her spousal benefit does not alter her survivor benefit. Any reduction in spousal benefit due to age (below FRA) does not apply to or affect her survivor benefit.
I had pondered this exact question for a number of years. I was told that if my wife took spousal benefit prior to her FRA that her age at that time would not affect how her survivor benefit was determined: in other words, if her spousal benefit was subject to a reduction due to her age then this situation would not determine her survivor benefit in any way, (1) if she later collected a survivor benefit before her FRA then the reduction in benefit would be based on her age at that time, or (2) if I died after she was at her FRA then there would be no reduction in her survivor benefit.
That's what I was told 8 or 10 years ago and for a couple years now I have been trying to formally define this using the rules of the SSA; I didn't want to blindly trust internet forums and media articles. It has been difficult to find the particular SSA rules that would address this case but I think they are there.
But first, I'll point you to a thread from only a week or two ago where this same question was asked and I replied. See https://community.aarp.org/t5/Social-Security/Husbands-delayed-retirement-benefit/m-p/2489117
I will add to my discussion in that thread with a few additional remarks.
(1) The "deemed filing" rules do not apply to survivor's benefits. This is stated in SSA POMS # GN 00204.035 Deemed Filing on the SSA site at https://secure.ssa.gov/poms.nsf/lnx/0200204035. See the second paragraph (below the bullet points) under Section B. "Deemed filing does not apply to survivor benefits."
(2) POMS # RS 00207.005 Widow(er)'s Benefits - Conversion of Benefits - Policy, addresses conversion of spousal benefits to survivor's benefits. Section C states "When a claimant is entitled to spouse's benefits as a legal spouse and notice is received that the number holder (NH) died, both benefits are terminated." See https://secure.ssa.gov/poms.nsf/lnx/0300207005
The conclusion from these two rules are that the clock resets once survivor benefits begin. No prior claiming or age at claiming is relevant. So if the spouse, now survivor, is below their FRA and they take survivor benefits the benefit will be reduced for their age at that time (and the reduction factors are not identical to the spousal reduction factors) or if they are now at their FRA or older there is no reduction in benefit regardless if the spousal benefit had been reduced or not.
(3) Spouses (survivors) who have their own SS retirement benefit and yet are collecting a spousal benefit may elect (even in these days of the deemed filing rule) to put the survivor benefit in abeyance until FRA and meanwhile collect only their own work benefit. My own spouse cannot take advantage of this special rule since she has no work history and in this case the rules do not permit postponing the survivor benefit. I don't recall the form number at the moment but I could if asked. Some survivors might benefit from this rule. And I suppose the reason that it still works now is because that one POMS states that deemed filing doesn't apply to survivor benefits.
Edit to add: I would have thought this was an easy question. Certainly there must be hundreds of people actually in this situation. If not thousands or even hundreds of thousands. A few million even! But I have seen little discussion of this. A few years ago I even joined a "widow/widower" group on Facebook, certainly those folks would know! But I never saw any discussion of this question; I recently asked it there myself and got replies from only 2 people and they didn't really know the answer. I then called the SSA and asked them and was given a lot of garbage. At that point I wrote to Ask Larry and got what is, to me, a pretty much definitive answer. I have found discussion in a few other sources, a scholarly legal reference book and some other sources. But still my mind wants to see it clearly documented in the SSA POMS or the CFR. But I think the two POMS discussed above are enough to create the logic trail.