Well, since she was killed and now an Einherjar, she sparred with them and she was a warrior, that was the offer.. She isn't a Valkyrie.
That she is an Einherjar
now does not in any way, shape, or form mean she couldn't have become a Valkyrie
before.
It's like you're arguing that because Harry ended up the Winter Knight, he couldn't possibly have become a Denarian and Lasciel wasn't offering to make him one. Ending up as one thing does not mean one couldn't have become another thing if they'd chosen differently.
Gard's offer was clear from the context of the series, our knowledge of Gard, and the scene. She was not offering to make her Einherjar there -- to be Einherjar, you have to die. Einherjar are also never referred to as "security consultants." The only characters referred to as such are Valkyries like Gard and Freydis. Gard's own words were offering Murphy the same job that Gard herself identifies as having, a job that is clearly code within the series for "Valkyrie."