Of course you're not cruel, you're doing the best you can for your baby, just like we all are!
If your dd (that's darling daughter in mumsnet-speak!) starting feeding every 2 hours again, it was probably because she's having a growth spurt so needs extra nutrition. IT's happened with my dd a number of times, I find it best just to weather the extra feeds for a while until it gets back to normal.
19 weeks isn't ideal for weaning, current advice is to wait until 6 months, but it's not uncommon either (it's past the absolute minimum of 17 weeks). One problem is that milk (breastmilk or formula) has a lot more calories in than baby rice, so the baby rice will make your dd feel full but not give her as much nutrition.
The current NHS advice about weaning is here.
There are signs if your baby is ready to wean, she needs to be able to hold her head up, sit well, gained a healthy weight (some people say doubled their birth weight), make chewing motions well enough to move food around their mouth, and is showing an interest it what you're eating (such as watching, trying to touch). If your dd isn't meeting all these I'd be inclined to go back to giving just milk until she is.
Can you speak to your hv (health visitor) for some advice specific to your dd?