Baptisms only use first and middle names for the one being baptised.
For example, two entries above Sarah, there is John West, son of Richard and Elizabeth Hughes. West would be his middle name. If you flip through the pages, you will see more examples.
FindMyPast has two indexes done for Sarah's entry. One is done as Sarah Baxter, surname Jarvis.
However the second one is indexed as surname Baxter, possibly because it is odd the mother's first name appears to be unknown.