Dig in! The only sure fire way to remove crab grass amidst the flowers is to use a digging fork and dig out the invader roots and all. I know, this is not what you wanted to hear so another option is to use an herbicide, either a non selective herbicide like RoundUp that kills all plants or one made for crabgrass such as Halt. The problem is making sure the herbicide does not get onto your flowers. Some gardeners have used boiling water poured onto the crabgrass clumps to kill it. Again you may harm your other plants and boiling water also kills the tiny soil pathogens that the food chain needs.  Make sure there is a border to keep your lawn grasses from sneaking into the flower beds and use a mulch 2 to 3 inches deep around the flowers to keep out new crabgrass and to keep crabgrass from returning. There is one more solution - move to a new home without any crabgrass for miles around. Gardening can be a challenge but hang in there - you notice  those weeds and other imperfections more than anyone else.   Keep growing, but not crabgrass, Marianne Binetti