90后 - 90hòu - born in the 90s / the 90s
女孩 - nǚhái - girl
月 - yuè - month
减肥 - jiǎnféi - to lose weight
斤 - jīn - jin (unit of weight equal to 500g)
减 - jiǎn - to lower / to decrease / to reduce
朋友 - péngyou - friend
笑 - xiào - smile / laugh
胖 - pàng - fat
高兴 - gāoxìng - happy
跑步 - pǎobù - to run / to jog

Measure Word - Expressing the number of sth with an object specific measure word in the form of "Number + Measure Word + Noun" (if the number is one, you can omit it and use the measure word by itself)
90后女孩三个月减肥45斤
有一个90后女孩，她的名字叫妃妃（Feifei），三个月里减了45斤。
三个月里，她每天五点去跑步。

(在)...里 - Expressing "in / inside…" with "(zài)...lǐ"
三个月里减了45斤。
三个月里，她每天五点去跑步。

Verb / Verb Phrase + 了 - Expressing that an action has been completed with "Verb / Verb Phrase + le"
三个月里减了45斤。

两 (+ Measure Word) - Expressing the number "two" when specifying quantities with "liǎng (+ Measure Word)"
两年前她155斤，她的朋友们笑她太胖了，她很不高兴。

Time or Verb Phrase + (以)前 - Expressing "before" a specific time or action with "Time or Verb Phrase +(yǐ)qián"
两年前她155斤，她的朋友们笑她太胖了，她很不高兴。

Noun + 们 - Expressing the plural form of a noun with "Noun + men"
两年前她155斤，她的朋友们笑她太胖了，她很不高兴。

太 + Adj. (+ 了) - Expressing "too" to indicate excess with "tài + Adj. (+ le)" (negative formed with 不太 + Adj.)
两年前她155斤，她的朋友们笑她太胖了，她很不高兴。

Noun / Pronoun + 很 + Adj. - Expressing "very" or to link a noun or pronoun and an adjective with "Noun / Pronoun + hěn + Adj." (sometimes the 很 is translated as "very" but often it is a link between a noun and an adjective)
两年前她155斤，她的朋友们笑她太胖了，她很不高兴。
现在她很高兴，因为她减了45斤。

每 + 天 / 周 / 年 / 次 - Expressing "every day / every week / every year / every time" with "měi + Time Word" (天, 周, 年 and 次 act as their own measure words)
三个月里，她每天五点去跑步。

Hour X + 点 - Expressing "X o'clock" with "Hour X + diǎn"
三个月里，她每天五点去跑步。

Result，因为 + Reason - Expressing "because…" to explain the reason with "Result，yīnwèi + Reason"
现在她很高兴，因为她减了45斤。