Your question is an important one because it points to two different but overlapping issues that are common in working with students with LD. Working memory is often an area of challenge for those with LD and while there are lots of strategies purported to "fix" or "repair" these weakness, consumer beware, because this is an area where much more research is needed. And if numbers are of particular concern, I bet your daughter's struggles are much more involved than just memorizing math facts or procedures. They probably stem from difficulties understanding the underlying concepts in math (think about your daughters answers - or guesses- and ask yourself if she seems to have a good grasp of what could be referred to as an internal number line)
Working memory (also called active memory) is one of the many "executive functions" that we rely on to help us learn and remember information. It is a system that is constantly being updated, enabling a person to capture new information, determine whether it is important or irrelevant, and make needed “shifts” in cognitive set (the way we think about something). Depending upon what enters the active memory system, we are constantly (and rapidly) updating, inhibiting, generating, and set shifting. (it’s easy to see how any upset to this system, perhaps caused by LD, can result in problems with learning)
An Example of how working memory operates: think about a game of chess, checkers or bridge, where players start out with certain plans or assumptions and need to update their information (immediate and several moves ahead) in order to be successful. This constant shifting of thinking, based on new information that is being made available (by opponent moves as well as gestures, non-verbal cues, assumptions about the speed of players moves, etc) makes it clear how critical (and potentially fraught with problems) and area this is.
So what does this have to do with your daughter's academic success?
The more capable/skilled she becomes in a particular area (such as reading or math) the less effort she will need to expend on keeping her memory skills in tune. It might help to focus just on building memory skills, but try to do this in the context of skills learning. Play card games that require remembering what cards have already been used. Do simple sudoko -like puzzles (start with VERY simple ones to build confidence and ensure success). Encourage her to create "cheat sheets" that will help her get to math answers more easily (her creating them herself will serve as a teaching tool and help her learn and build skills in a very personalized way).
You should DEFINITELY work closely with your daughters teachers to figure out how to help her overcome some of her struggles in this area. A really good book (more for educators, but perhaps helpful to you as well) is Teaching Math Meaningfully: Solutions for Reaching Struggling Learners by David Allsopp, Maggie Kyger and LouAnn Lovin (Paul Brookes Publishers, 2007).