Since you'll have at least eight (and as many as 12) SWUs, I'd use some of those before I'd spend all my redeemable miles on an award ticket.

To check for upgrade availability, check out www.expertflyer.com and look for C inventory (coach to biz upgrades). Subscription is cheap and well worth it.

Even without status, if C is available when you book the ticket, upgrade can be confirmed right then. I'd advise flexibility (required no matter what method you use to get her into biz class) when booking the tix. If her dates/times are set in stone, there's a strong chance she might end up in coach. Flexible plans = much larger chance she's comfortable in Business Class.