Names
Reiko Tamura was introduced in the series as Ryoko Tamiya, the name of her host. The names sound similar, and they should. They use some of the same Kanji (a system of Japanese writing using Chinese-derived characters). Hitoshi Iwaaki could have written same-sounding names a number of different ways, but he chose to write them with particular Kanji. I've analyzed both names using the Kanji he chose.
Ryoko Tamiya
Using the Kanji Iwaaki used for Ryoko Tamiya, 
, Ryoko means “good child” and Tamiya means “rice field palace”. I don't think these meanings are important or insightful to Reiko's character. The only thing I can think of is the second part of Tamiya that means palace. Ryoko's body is a sort of palace for Reiko who took it over, so it sort of makes sense, but I think it's stretching it. I definitely can't see a rice field being of any importance.
Reiko Tamura
The name Reiko Tamura, 
, that she uses throughout most of the series is the one, I think, where the Kanji is important. The Kanji Iwaaki uses to write Reiko Tamura means “jewel child” and “rice field village” respectively. The word child is interesting because a little before her death she referred to herself as humanity's child. I think the word refers to offspring and not age, although both would work considering how young the parasites are. It basically implies she came from someone or something, and throughout the entire series Reiko constantly questions where she came from.
A jewel is defined by Webster as “a person or thing that is treasured, esteemed, or indispensable.” Reiko is highly looked at by other parasites and is sort of the central element in learning to coexist with humans. She certainly is the brains in her group; it's she who understands humanity best, and I think that makes her indispensable.
The name Tamura is especially interesting because a rice field is random in analyzing Reiko's character, but it uses the exact same first Kanji (and sound) as “Tamiya.” Migi comments later in the series that Reiko probably would choose a name similar to her host's if she changed her identity, as names aren't important to parasites. This “rice field” is the similarity. I like that the Kanji attached to “rice field” means something else that can be resided in like a palace. Reiko took over and is essentially living in and through Ryoko's body. The Kanji make that fact pretty interesting.