Aw, so sorry to hear Amber is not well

May I ask is the cause of her diarrhoea ?
If it's too much veggies, then obviously you need to omit for a few days. Is she on an antibiotic as this can wreak havoc on their little tums ? Critical Care is good for piggies who are not eating for themselves as it contains all the nutrients a piggy needs but you need to be cautious as hand feeding them will often make them forget how to do it for themselves (they become lazy)
I would go with the instructions, mix to a paste consistency and give it to her via a small spoon. Mine have taken it from my finger but others have had to be syringed if they've been really poorly.
Weigh Amber to keep a check, this is critical so you can gauge weight loss/gain etc.
I think the going rate of CC is 120mls per 24 hours so if you feed her 10mls every 2 hours, should be sufficient. If she takes more, then you could reduce the feeds. This is what I have done for an adult poorly piggy, not sure how old Amber is if she is only 400g - she is very young I assume ? Always give her a good brand of pellets and fresh water too.
I empathise totally (been there a few times :...) but it is so important to keep her gut moving and prevent stasis as this can be fatal. Keep her on the feed until she is eating for herself or has reached her target weight. Maybe give her a Vitamin C supplement if she's not having fresh veggies, soluble tablets are available from most supermarkets/pharmacies for £1+.
Please keep us informed and we're all here to help if you have any worries

Hugs to Amber x>>