Here are a couple of options, depending on the formality of your interaction:
Informal:
* 你好,卡拉! (Nǐ hǎo, Kǎ lā!) - This is the most common and straightforward way to say "Hi Karla."
* 卡拉,你好! (Kǎ lā, nǐ hǎo!) - This is also a common greeting, placing Karla's name first.
Formal:
* 卡拉女士,您好! (Kǎ lā nǚshì, nín hǎo!) - This is a respectful greeting that addresses Karla as "Ms. Karla."
* 卡拉先生,您好! (Kǎ lā xiānshēng, nín hǎo!) - This is a respectful greeting that addresses Karla as "Mr. Karla" (if applicable).
Remember, when using a person's name in Chinese, it's usually written in pinyin, the romanization of Chinese characters.