Was the pic taken right after she was fed? If so, you may want to feed her more.... Otherwise, it depends a lot on Arwen (nice name by the way). 
A lot of people will tell you the "body width rule" which I won't use because I don't trust it - using that rule, I had a rat snake mutt hybrid (pet only) that actually tore the webbing at the edges of her mouth one time. Every time I fed her after that, the scars kept tearing, so the resolution was to only feed her many SMALL meals. That solved the problem, but the poor girl never looked the same. Because of that experience, I am VERY cautious about the size of prey items I will offer.
I know a reptile vet who has suggested feeding small meals (single prey items) about 4 days apart. I personally prefer a couple of prey items about a week or so apart, as you are doing. It's up to you.
Also, you may wish to consider young rats (comparibly sized of course). They may be priced about the same as mice, or radically different, depending on your supplier. My theory here is that young rats whose bones have not yet ossified (completely hardened), and don't have much fur yet, may be more digestible.
Good luck, I hope this helps.
~Rebecca
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1.1 Ball Pythons (1.0 '05 Ghost, 0.1 '03 Normal)
0.1 Dumeril's Boa
0.2 American Pit Bull Terriers (40 lb darling lap dogs)