Lambivac does not cover all the strains that heptavac does, so yes she would need two doses, 4-6weeks apart to be protected if you were to change to heptavac.
Bearing in mind the shelf life of a bottle of vaccine is 10 hours as they are very unstable, you will want to get your goats on the same as each other, and probably also find other keepers of small numbers to share bottles with.
Instead of changing the new one to heptavac, many goat keepers just use lambivac as goats tend to produce a poor response to clostridial vaccines and therefore many believe a good response to a few strains (those a goat is more likely to encounter) is better than a weaker response to all that are in heptavac. Also it is advised to vaccinate goats at least every 6 months instead of the annual boosters on the data sheet, many goat keepers do this every 4 months.
I'd recommend speaking to your vet, and reading the British goat Society's recommendations to decide what would be best for you.