Voluntary redundancy question

Hi.

First time poster but hoping you can help me.

I have been with my company for 19 years. At first I loved it. Then we got outsourced and now i have manager about 200 miles away, never comes over to see us, and rarely speaks to us. I used to have quite a technical job but now it's pretty much data input which is fairly soul destroying.

The company offered expressions of interest for voluntary redundancy. I applied as did 2 others in my team. I have been refused due to my skill set. My colleague who has more experience on the current system has been accepted even tho she admitted to the manager that she onky applied to see what the figures were like. The other colleague is currently on leave so I don't know their situation.

So I have many questions...
1) can they differentiate like that,? We have pretty much the same service length, same skill set (altho theirs is better on the current system), we got the same appraisal marking etc etc.
2) in the last 3 years i have been off twice on long term sick with stress, anxiety and depression. I reckon that they think i will walk out of the job so saving a redundancy pay out. Can they do this?
3) i have gone to our union and am hoping to appeal the decision but is this likely to happen?

No one at work can understand their decision. I know they can choose basically who they want to go and who they don't but I honestly feel that they are wanting me to walk out. My problem is is that i can't afford to do that as I won't get the same pay for number of hours elsewhere and i have childcare costs to pay for. so I am currently looking at staying in a job that I have been utterly deskilled in for another 18 months at least until my youngest starts school whilst my colleague who 'isn't even sure she wants to go' could leave at the end of August.

Any advice would be greatly appreciated. I am utterly heartbroken at this decision.