Yes, I think she would have offered Spike her blood at this point in the series. She pretty much was the captain of the I trust Spike team and was focused on the impending war more than anything else so I don't see her putting much thought into it past "I trust him". If this was something she could have done to make her army stronger then yes, she would have offered to do it no matter what the risk. Based on her actions in s7 I don't see any reason why she wouldn't trust Spike with this.
I know you didn't ask this question but...I don't think Spike would have taken her up on that offer.
