Shields aren't designed to protect your nipple from pain or damage (infact a badly fitting one can cause damage, and if your baby struggles to get a wide open mouth they can make it harder to get a deep latch) BUT if you find a good fit and it does help with pain then obviously you can choose to use it this way.
Have you got any access to a board certified lactation consultant? In the UK, LLL, ABM, NCT etc all offer free advice, some free home visits, and are really the best people to talk to about how to get back to breastfeeding.
If baby is frantic with hunger at breast, then calming her with a small amount of formula or pumped milk may be a good start (try half an ounce maybe?). However you can also try introducing baby to your breast before she gets really really hungry. She may not take loads at first but you are creating the connection in her head that this is where milk comes from while she is nice and calm.
Re the damage, if it is still there at 3 days and not healing you should get a swab for infection. If it is healing but you are afraid of opening it up again, then you need to find the root cause of the damage. Is she uncomfortable lying on one side (common in forceps babies - can be helped by osteopathy etc.), can you try different positions to mimic feeding from the other breasts, or just to give damaged parts of your nipple a rest (I fed in all sorts of angles just to move the pain around to a new part of my breast!). I think I have recommended laid back breastfeeding/bio nurturing before but it really can help get baby back to their natural breastfeeding instincts and latch can be deeper and less painful because baby is always tummy to tummy with their chin meeting the breast first.
Re pumping. If you feed any formula, you should try to pump an equivalent bit of breastmilk (it is hard to say how much because they aren't equivalent substances - a breastfed baby eats less breastmilk than a formula fed baby eats formula) to tell your body how much baby needs. Feeding/pumping regularly at night is important for keeping your supply up too, if you think you can face it for a short period. When I was supplementing and pumping the aim was to pump of feed baby directly from breast every 2hrs or less if she asked but that was cos my Los weight was low. An LC really is the best person to talk to if you can.