Numerology works from the premise that people and things are named exactly as they should be. You might dislike your parent's choice for you, but for some reason, your name is exactly as it was meant to be. This same sense of destiny underlies a "married" name -- if a woman is drawn to a man enough to make a lifelong commitment, then the name she creates in recognition of this commitment will also fit her personality. It may even be more beneficial!
Most Numerology experts would tell you to find out what your Core numbers will be if you do decide to change your name, and it's entirely possible that a person's married name will give numbers that increase their chances at success by making them more outgoing or more creative. It might be clear to this person that her new, married name is in some ways numerologically "superior" to her birth name. But most Numerologists agree: the numbers will work best in your favor when you take a step back, armed with all the facts at hand -- not only the numbers of all name options, but also your feelings about marriage and commitment, your feelings about your partner's family, your comfort level at changing your name and whether you even like this new name -- and make a decision from that point. Whatever you decide, the numbers will then work more in your favor because it's much more likely that the name you choose is the one you were meant to have.
For all the right reasons
It's important to look at two types of name changes: "organic" and "artificial." "Organic" name changes happen as a part of a person's personal growth -- nicknames, for example, or married names. A person's stage name or pen name (or any other kind of professional name) is also considered an organic name change, since it helps further them on their life's path. When people change their name in this way the change of moniker is organic, even though it is deliberate.
Meanwhile, an "artificial" name change is a bit more manipulative. For example, if a Numerology expert told you that changing your name (or even just the spelling of it) would bring you wealth or greater success, this is an artificial name change because it was not spurred by a greater, more concrete goal. (For example, the goal to become a recognizable musician or to have a harmonious-sounding author's name to put on your published novel).
But artificial name changes -- simply to get more 1s or 3s or 8s in your name, because you believe this might be beneficial to you -- indicate that you skipped a step or took an easy way out. In other words, they do not happen naturally as a part of your growth, and can bring more problems than solutions.